This invention relates to liquid level transducers, and more particularly to a liquid level transducer having a magnetic float that moves in response to a change in liquid level.
U.S. Pat. No. 3,815,416 to Dean et al. discloses a prior art apparatus for indicating the level of liquid in a tank car. The apparatus includes a float encircling a guide tube extending down into the tank. The float is magnetically coupled to a gauging rod which bears indicia representing the level of liquid in the tank. The gauging rod is normally retained inside the guide tube via an upper cover removably secured to the tank opening. When it is desirous to check the liquid level within the tank, the cover is removed and the gauging rod is manually raised until it is magnetically coupled with the float. Depending on the liquid level, the length of the gauging rod extending out of the tank will change. The user can ascertain the level in the tank by the visible indicia of the rod. The apparatus also has a mechanism for automatically visually and audibly alerting the user when the level has reached a particular level, such as a near full condition when the tank is being filled. This mechanism includes a tower and a series of reed switches mounted on the tank above the rod opening. A magnet attached to the top of the rod moves past the reed switches to serially actuate them as the tank is filled.
Although such systems are adequate for their intended purpose, they are quite unwieldy, relatively expensive, and require the user to gain access to the top of the tank before a measurement can be taken, which can be both time consuming and dangerous. Moreover, with these types of systems, it is not possible to determine the level of liquid in the tank from a remote location and/or when the tank is in transit.
Moreover, prior art guide tubes are typically filled with antifreeze or the like which surrounds the gauging rod to provide some resistance against movement when the gauging rod is decoupled from the float, such as when the tank is traveling and subjected to rail or road conditions that otherwise may cause the gauging rod to bounce within the guide tube. Unfortunately, the coolant can leak into the area that holds the magnet, thereby destroying the magnet and causing expensive replacement in terms of both components and time, and possibly resulting in less accurate readings, or no reading at all depending on the level of damage to the magnet.
In addition, due to the relatively weak magnetic coupling forces between the float and gauging rod of the prior art, the capacity to obtain consistent readings is diminished, hysteresis is relatively high, and more especially when coolant or other fluids enter the magnetic coupler of the gauging rod thereby changing its weight and the coupling height with the float.
Also, prior art gauging rods are prone to frictional wear and eventual failure as they slide up and down inside the guide tube in response to changes in liquid level and/or a user pulling the gauging rod upwardly to couple with the float or remove the gauging rod from the tank, and pushing the gauging rod downwardly to its seated position. Since a relatively large gap exists between the prior art magnetic coupler and the guide tube, the gauging rod may not couple efficiently with the float since it may be oriented at an angle other than coaxial with the guide tube. Accordingly, both the accuracy and the coupling forces may be compromised.
It would therefore be desirable to overcome one or more disadvantages associated with prior art liquid level transducers.